In recent years, for the purpose of energy saving and downsizing, light-emitting devices (LED flash) using a light-emitting diode (hereinafter referred to as “LED”) as the light source have been increasingly used as a light-emitting device for an image pickup camera. A well-known example of such light emitting devices is a light emitting device using a combination of an LED and a fresnel lens.
In general, the imaging region of an imaging camera is square. Therefore, a light-emitting device preferably illuminates the illumination region in a square shape to obtain clear captured image. In view of this, desirably, a fresnel lens used in a light-emitting device for an imaging camera uniformly and efficiently illuminates a square illumination region with light emitted from a light emitting element. Conventionally, various fresnel lenses for illuminating a square illumination region have been proposed (see, for example, PTL 1).
FIG. 1A is a perspective view of fresnel lens 10 disclosed in PTL 1. Fresnel lens 10 illustrated in FIG. 1A can provide a function same as that of cylindrical lens 20 illustrated in FIG. 1B. As illustrated in FIG. 1A, in fresnel lens 10 disclosed in PTL 1, a plurality of rectangular grooves 12 are concentrically disposed with a space therebetween in plan view.